The present disclosure relates to a method fir improving startability of a vehicle, said vehicle being provided with a prime mover and a kinetic energy recuperation system. The prime mover is adapted to propel the vehicle either alone or in combination with the kinetic energy recuperation system which is operably coupled to the prime mover and to wheels of the vehicle and is adapted to store energy at times when there is an abundance of energy and to consume energy at times when there is a demand for energy. The pre-sent disclosure also relates to a vehicle which utilises the method according to the invention.
In the automotive industry the general trend is and has been to reduce fuel consumption end exhaust gas emissions in the vehicles, especially in commercial vehicles having internal combustion engines. This may be achieved in many different ways. One strategy has been to reduce the engine size in general. However there may be times when such a downsized engine is not sufficient to deliver the required torque to propel the vehicle. Especially when the vehicle, such as a commercial vehicle in cargo traffic or a construction type of vehicle, is heavily loaded. In combination with a downsized engine also a secondary and further assistance motor(s) can be implemented, which is (are) adapted to assist the main engine at times when the power demand delivered by the main engine is insufficient.
For vehicles running on frequent stall/stop cycles, enough torque must be delivered from the engine or system of engines to achieve proper startability. It should be noted in this regard that “startability” is meant as the take-off of the vehicle from a general standstill, not that the engine or system of engines is started up for the first time, such that the engine or system of engines is cold when started. When downsizing an engine to reduce fuel consumption or reduce exhaust gas emissions, the downsizing cannot be made to such extents that take-off from a standstill or acceleration on a general basis is impaired unless secondary assistance propulsion systems are provided.
Using Automated Mechanical Transmissions (AMT) instead of traditional Automatic Transmissions (AT) can also save fuel in a city bus, local distribution and refuse truck applications. To keep weight, cost and size of the transmission low, it is an advantage if an AMT with a narrow ratio coverage and a low number of gears can be used. However, an AMT would normally not have a torque converter, as is the case for an AT, and in combination with a narrow ratio coverage it can lead to poor startability from a standstill of the vehicle. However, not only an AMT with for example only six gears, but any type of transmission having a narrow ratio coverage between the lowest and the highest gear might suffer from poor startability.
One way to complement a downsized internal combustion engine may be to utilize for example a flywheel which is loaded with kinetic energy when braking the vehicle. This energy may later be consumed as support for the engine when the vehicle needs extra propulsion, such as when taking over another vehicle or starting from a standstill. In this respect a flywheel gives little energy at a high power which means that it is quickly loaded but also as quickly unloaded. This is in general terms the opposite situation as for a battery.
US 2010/0280712 discloses a vehicle being provided with a flywheel in combination with an internal combustion engine. The vehicle engine is supported by the flywheel at times when extra torque is needed. In a first mode the vehicle is cruising and the flywheel has not yet been started. When the driver of the vehicle demands a deceleration, this deceleration is used to charge the flywheel. The energy in the flywheel may later be consumed to support the internal combustion engine for propulsion of the vehicle. In a start-up mode, when the engine is cold, the internal combustion engine is run together with the flywheel in order to warm up the internal combustion engine quicker, which improves the exhaust gas after-treatment efficiency more rapidly. As a result, exhaust gas emissions are more rapidly reduced. The energy thus stored in the flywheel may later again support the internal combustion engine for propulsion of the vehicle.
It is desirable to further improve the startability of a vehicle, especially of a vehicle in which a prime mover has been supplemented with a kinetic energy recuperation system for the possibility to reduce the size of the prime mover.
According to a first aspect a method is disclosed for improving startability of a vehicle, said vehicle being provided with a prime mover and a kinetic energy recuperation system. Said prime mover is adapted to propel the vehicle either alone or in combination with the kinetic energy recuperation system which is operably coupled to the prime mover and to wheels of the vehicle and is adapted to store energy at times when there is an abundance of energy and to consume energy at times when there is a demand for energy. The method comprises the steps of:                determining that the vehicle is standing still or essentially standing still,        detecting a take-off assistance condition,        detecting a level of energy in the kinetic energy recuperation system,        if the level of energy is found insufficient, connecting the prime mover to the kinetic energy recuperation system and running the prime over such that energy from the prime mover is stored in the kinetic energy recuperation system, and        when the driver requests the vehicle to take off, running the prime mover and consuming energy from the kinetic energy recuperation system such that the wheels of the vehicle initiate propelling thereof.        
The method safeguards that there is enough energy in the in kinetic energy recuperation system for a proper take-off from a standstill condition. This safeguard aspect is particularly relevant for vehicles such as city busses or refuse trucks which drive many hours a day, and often take off from a shorter or longer standstill. A standstill of the kind relevant, for the inventive method may include for instance when the vehicle, such as a passenger bus in regular city traffic, regularly is stopping at bus stops to let people on and off. The time standing still at the bus stop is generally rather short in the sense that although the bus may be provided with a start/stop function, the engine and exhaust gas system are generally still warm enough to still be efficient and to produce low emission levels when again starting the engine to drive away, i.e. to take off from the bus stop. A method of the kind defined is particularly advantageous for a vehicle having a downsized engine, but may well be utilized in combination with any type of engine. The method thus improves the startability of the vehicle, enabling, smooth interaction with the surrounding traffic, as well as increased life-length of the transmission clutch. By the expression “to consume energy” is meant the reuse of energy that earlier has been stored in the kinetic energy recuperation system.
According, to one embodiment, the step of finding the level of energy insufficient involves finding that the level of energy is lower than a first predetermined energy value.
The kinetic energy recuperation system may be loaded to the level of a first predetermined energy value, which first predetermined energy value is chosen such that the vehicle may take off smoothly at most occasions. The first predetermined energy value need not represent maximum loading. The first predetermined, energy value ma either be a fixed value, or be adapted to each particular take-off. Hereby a flexible system may be achieved.
According to one embodiment, if the level of energy is lower than said first predetermined energy value, the method further includes detecting whether the prime mover is running, and if it is not, starting up the prime mover.
This is particularly relevant if the vehicle is provided with a start/stop function. It also comes into effect if the prime mover for some other reason has been stopped.
According to one embodiment the vehicle is provided with a start/stop function, such that if a take-off assistance condition is detected and if the vehicle is standing still or essentially standing still, said start-stop function is disabled from stopping the prime mover from running.
This way the method is able to quickly ensure that the kinetic energy recuperation system is stored with energy such that the vehicle is ready to take off quickly.
According to one embodiment of the invention the steps are performed in the order mentioned.
According to one embodiment the step of determining a take-off assistance condition includes any one or a combination of the following: determining that the vehicle is standing in or at an upward slope, determining that the vehicle is heavily loaded, or determining that the vehicle is being belated in relation to a desired schedule.
According to one embodiment the step of determining that the vehicle is standing in or at an upward slope involves using inclination detecting means and determining if the inclination detecting means detect an upwards slope being equal to or greater than a predetermined inclination value.
Such inclination detecting means may include an inclination sensor located in the vehicle, a vehicle navigation system such as a Global Positioning System (GPS) having also information of altitudes included, or a vehicle navigation system such as a GPS system which is adapted to record the altitude of a position if the vehicle passes said location in order to use the altitude information the next time the same location is passed.
According to one embodiment said predetermined inclination value corresponds to an upward slope of 7.5%, preferably of 10%, and more preferably of 12.5%.
According to one embodiment the step of determining that the vehicle is heavily loaded involves weight sensing means and determining that the weight sensing means detect a payload in the vehicle being equal or greater than a predetermined weight value.
Such weight sensing means may include gauges of different kinds located in or at a vehicle suspension system, such that the additional payload on the suspension system may be estimated in relation to the vehicle dead weight.
According to one embodiment said predetermined weight value corresponds to a payload of 30%, preferably of 50%, and more preferably of 70% in relation to a vehicle dead weight.
According, to one embodiment the method further comprises prohibiting propelling the vehicle until the level of energy in the kinetic energy recuperation system is equal to or greater than a second predetermined energy value.
In such a case the kinetic energy recuperation system should be loaded up to the second predetermined energy value before allowing take-off of the vehicle. An example may be loading of the kinetic energy recuperation system to an energy level of 200 kJ in order to add 100 kW during 2 seconds to the take-off energy provided by the prime mover.
According to a second aspect a vehicle comprising a prime mover and a kinetic energy recuperation system is disclosed, such that said prime mover is adapted to propel the vehicle either alone or in combination with the kinetic energy recuperation system, which is operably coupled to the prime mover and to wheels of the vehicle is and adapted to store energy at times when there is an abundance of energy and to consume energy at times when there is a demand for energy, the vehicle being adapted to perform the inventive method.
According to one embodiment the kinetic energy recuperation system is a flywheel.
This is a type of kinetic energy recuperation system which is quickly loaded, i.e. which stores energy quickly, but which at the same time makes the energy available for consumption by the vehicle.
According to a third aspect a vehicle is disclosed in which the prime mover is an internal combustion engine.